A bipartisan delegation of U.S. senators visiting Afghanistan on July 4 called for a new strategy from the Trump administration to turn the tide against an increasingly strong Taliban insurgency and end the longest U.S. war.

The delegation, led by Senate Armed Services Committee Chairman John McCain, was in Kabul on a regional trip that included two days in neighboring Pakistan.

"None of us would say that we are on a course to success here in Afghanistan," McCain said at a press briefing at NATO's headquarters in Kabul.

"That needs to change, and quickly," he said. "The strongest nation on Earth should be able to win this conflict."

The Pentagon is currently reviewing strategy in Afghanistan, where U.S. troops have been backing the fight against the Taliban for 16 years. It reportedly is considering recommending an increase in troops of 3,000 to 5,000.

But McCain (Republican-Arizona) and other senators suggested that an incremental increase in troops would not be enough. McCain was accompanied by Senators Lindsey Graham (Republican-South Carolina), Elizabeth Warren (Democrat-Massachusetts), Sheldon Whitehouse (Democrat-Rhode Island), and David Perdue (Republican-Georgia).

The Taliban is "not going to negotiate unless they think they are losing," McCain said. "So we need to win and have the advantage on the battlefield and then enter into a serious negotiation to resolve the conflict."

McCain made a mark in the last decade by urging a "surge" in U.S. troops to win the war in Iraq before negotiating a peace accord there -- a strategy adopted by former President George W. Bush that was credited with success at putting down the insurgency in Iraq at the time.

Senator Lindsey Graham said he would tell U.S. President Donald Trump that 8,600 American troops currently in Afghanistan "will not get the job done" and that more American troops along with more NATO troops should be deployed to "turn stalemate into success."

Since the exit of most foreign troops in 2014, Afghanistan’s U.S.-backed government has lost ground to the Taliban insurgency. A U.S. report found earlier this year that the Taliban controls or contests control of about 40 percent of the country.

Warren did not join with the others in pushing for more troops. She said she came to get "the view on the ground about what is happening" in Afghanistan.

"We need a strategy in the United States that defines our role in Afghanistan, defines our objective, and explains how we can get from here to there," Warren said.

Last month, Trump gave Defense Secretary Jim Mattis the authority to set American troop levels in Afghanistan, but as commander in chief Trump must sign off on an overall strategy for the war.

Mattis has said the strategy he will recommend, which will be presented to Trump by mid-July, will take a broader "regional" approach, with no set timetable.

U.S. security officials have privately said the most likely options will be to increase training and air support by 3,000 to 5,000 troops for still-inexperienced Afghan security forces, while also tracking down Al-Qaeda, Islamic State, and other Islamist extremists based in Afghanistan.

The commander of U.S. and NATO forces in Afghanistan, General John Nicholson, has said "several thousand" more foreign troops -- mostly trainers -- are needed to break a military stalemate with the Taliban.

In 2001, a U.S.-backed military intervention in Afghanistan toppled the Taliban regime, whose ultra-hard-line interpretation of Islamic law banned most women from public life and executed people not seen as sufficiently pious, such as men who had beards not considered long enough.